Automatic dependent surveillance-broadcast (ADS-B) is a surveillance technology for tracking aircraft as part of the Next Generation Air Transportation System (NextGen). The United States will require aircraft operating within its airspace to be equipped with some form of “ADS-B Out” by Jan. 1, 2020. ADS-B, which includes two different services, “ADS-B Out” and “ADS-B In”, will replace radar as the primary surveillance method for controlling aircraft worldwide. ADS-B enhances safety by making an aircraft visible to air traffic control and to other appropriately equipped ADS-B aircraft with identity, position and velocity data transmitted at least once every second. It also provides the data infrastructure for inexpensive flight tracking, planning, and dispatch. The system relies on two avionics components—a high-integrity GNSS navigation source and a datalink (ADS-B transponder). There are several types of certified ADS-B data links, but the most common ones operate at 1090 MHz, essentially a modified Mode S transponder, or at 978 MHz (USA only).
At the present time, two link solutions are being used as the physical layer for relaying the ADS-B messages: (1) Universal Access Transceiver (UAT), and (2) 1,090 MHz Mode S Extended Squitter (1090-ES). A UAT is a data link intended to serve the majority of the general aviation community. The data link is approved for use in all airspace except airspace above 18,000 ft. UAT is intended to support not only ADS-B, but also Flight Information Service-Broadcast (FIS-B), Traffic Information Service-Broadcast (TIS-B), and, if required in the future, supplementary ranging and positioning capabilities. 1090-ES will support ADS-B and TIS-B. Both UAT and 1090-ES will allow aircraft equipped with “Out” broadcast capabilities to be seen by any other aircraft using “ADS-B In” technology as well as by FAA ground stations. Aircraft equipped with ADS-B In technology will be able to see detailed altitude and vector information from other ADS-B Out equipped aircraft.
The Federal Aviation Administration has announced a dual link decision using 1090-ES and UAT as media for the ADS-B system in the United States, with the 1090-ES ADS-B link for air carrier and private or commercial operators of high-performance aircraft, and UAT ADS-B link for the typical general aviation user. With 1090-ES, the existing Mode S transponder supports a message type known as the “extended squitter” (ES) message, which is a periodic message that provides 3-dimensional position (including altitude), velocity, time, and, in the future, intent. To enable an aircraft to send an extended squitter message, the transponder is modified and aircraft position and other status information are routed to the transponder. ATC ground stations and aircraft equipped with traffic collision avoidance system (TCAS) already have the necessary 1090 MHz (Mode S) receivers to receive these signals, and would only require enhancements to accept and process the additional extended squitter information.
All aircraft will soon be mandated to transmit ADS-B Out messages when moving around the world. Civilian unmanned aerial vehicles must also emit ADS-B to operate in the national airspace system. An ADS-B Out message of an aircraft contains the aircraft's 24-bit universal identity (e.g., International Civil Aviation Organization, or ICAO, identifier), global navigation satellite system (GNSS) precision position (including geometric altitude), barometric altitude, velocity, and time, and other flight trajectory spatial information. The ADS-B transmission of an aircraft occurs every second and reaches receivers beyond 100 miles from the aircraft. Consequently, anyone with an inexpensive ADS-B receiver can passively track in real-time each flight of each aircraft within the receiver's radio range, with high spatial and temporal precision. This ADS-B based flight tracking information can be misused by malicious entities targeting the aviation sector.
A problem addressed by the inventive system described herein is the possible misuse of ADS-B Out messages by attackers possessing cyber-attack tools, such as software-defined radio based ADS-B or GNSS signal spoofers or jammers, and physical attack tools, such as surface-to-air weapon systems. It is assumed these attackers are aiming to physically disrupt the air transportation system and unmanned aircraft (also called unmanned aerial vehicles, or UAVs) by attempting to destroy a targeted aircraft/UAV. ADS-B and GNSS spoofing/jamming, and surface-to-air weapon based threats are emerging threats for aircraft. Surface-to-air threats, for example, has been successfully instantiated on aircraft and UAVs at low altitudes (relative to terrain) or when a passenger/cargo aircraft is in critical flight phases in the terminal area (such as approach, landing, takeoff and departure). With technology advances, the range of surface-to-air threats may increase further in the future to threaten aircraft and UAVs during other flight phases and operations. By providing precise, high granularity, 4-D position information of each airborne aircraft and UAV, ADS-B Out messages may increase the exposure, likelihood, impact, and success of cyber threats, such as those from ADS-B and GNSS spoofing and jamming attacks, as well as physical threats, such as those from surface-to-air weapon attacks, to aircraft and UAVs.
The following references may be reviewed for additional background information (printed copies are being provided with an Information Disclosure Statement submitted with this application): (Ref1) Scott Stewart, “The Continuing Threat of Libyan Missles,” Stratfor.com, Security Weekly; (Ref2) Detlof von Winterfeldt and Terrence M. O'Sullivan, “Should We Protect Commercial Airplanes Against Surface-to-Air Missile Attacks by Terrorists?,” Decision Analysis vol. 3, no. 2, June 2006, pages 63-75; (Ref3) Federal Aviation Administration, “Automatic Dependent Surveillance-Broadcast (ADS-B) Out Performance Requirements To Support Air Traffic Control (ATC) Service,” Federal Register Vol. 75, No. 103, May 28, 2010; (Ref4) Sampigethaya, R. G. and Poovendran, R. and Bushnell, L., METHOD FOR VALIDATING AIRCRAFT TRAFFIC CONTROL DATA, U.S. patent application Ser. No. 12/841,349, 2010; (Ref5) Sampigethaya, R. G. and Poovendran, R., METHOD FOR PROTECTING LOCATION PRIVACY OF AIR TRAFFIC COMMUNICATIONS, U.S. Pat. No. 8,248,294 B2, Aug. 21, 2012.
As reflected in the background references noted above, no solutions for preventing misuse of ADS-B Out messages currently exist. ADS-B is intentionally designed to be unencrypted and openly accessible and beneficial to all systems operating in the airspace. Outfitting and maintaining the entire U.S. airline fleet with a military aircraft class of countermeasures that could foil missiles would be prohibitively expensive (e.g., cost over $40 billion), and the bulk of the civilian aviation fleet worldwide remains undefended today (see Ref2). Moreover, ADS-B provides a side channel for enhancing cyber and physical threats, and reducing the effectiveness and devaluing existing countermeasures.